build: corrected nsis uninstaller
doc: added motivations to THANKS
Using indexed bitmap for NSis
build: corrected --libs flags

Stuff to keep in mind:
- LDFLAGS are reserved for linker *flags*;
- LIBADD is a per-library variable and must include object/libraries to
  link library against;
- LDADD is the per-program version of LIBADD;
- external objects/libraries should be specified with -L and -l;
- internal objects/libraries should be specified directly (adding full
  path to .la for shared internal libraries);
- objects/libraries order is significative: any item can depend on the
  following items but not on the preceeding ones.
build: corrected flags for tests and demos
build: s/srcdir/abs_srcdir/

Changed srcdir to abs_srcdir to avoid unwanted resolution to the
repository dir in make distcheck. See issue #67 for details:

http://dev.entidi.com/p/adg/issues/67/
doc: general refactoring and improvements

Documented virtual methods in classes, added annotation glossaries,
removed warnings, improved building and a lot of other stuff to let the
documentation be build with less hassles.